1. Field of the Invention
The present invention relates to a detecting device that detects electromagnetic waves, a detector, and an imaging apparatus that uses the detecting device and detector.
2. Description of the Related Art
As a detecting device that detects electromagnetic waves from millimeter wavebands (30 GHz to 300 GHz) to Terahertz bands (300 GHz to 30 THz), a thermal detecting device or a quantum detecting device has been used. A thermal detecting device may be a microbolometer that uses material such as a-Si, VOx, or the like, a pyroelectric element that uses material such as LiTaO3, TGS, or the like, and a Golay cell, or the like. Such a thermal detecting device is a device that can convert electromagnetic wave energy into heat energy, and detect changes in thermoelectric power. While a thermal detecting device does not necessarily have to have cooling, heat exchange is used, so response is relatively slow.
A quantum detecting device may be an intrinsic semiconductor device that uses a semiconductor having no accepter or donor doping (MCT, photoconductive device, etc.) or an extrinsic semiconductor device that uses a semiconductor to which an acceptor or donor has been added, or doped. Such a quantum detecting device is a device that captures the electromagnetic waves as photons, and detects the photovoltaic power or resistance changes from the semiconductor having a smaller band gap. While response is relatively fast, the heat energy from the ambient temperature cannot be ignored, and so cooling is needed.
Thus, recently, as a detecting device having a relatively fast response and that does not have to have cooling, a detecting device that detects electromagnetic waves from millimeter wavebands to Terahertz bands, using an antenna and semiconductor rectifying device, has been used. This detecting device captures electromagnetic waves as a high frequency signal, rectifies the high frequency signal received by an antenna or the like with a semiconductor rectifying device such as a Schottky barrier diode or the like, and detects the current flow at that time.
With a detecting device using an antenna and a semiconductor rectifying device such as a Schottky barrier diode or the like, the function of an RC low-pass filter is formed of junction capacity Cj in the Schottky barrier and serial resistance Rs. That is to say, high frequency components of the signal are cut off by the function of the RC low-pass filter, which then cannot be detected by the detecting device. Therefore, the cutoff frequency serving as the upper limit of the frequency band beyond which the detecting device cannot detect has to be higher than the frequency band of the electromagnetic wave to be detected.
Now, the junction capacity Cj that makes up the RC low-pass filter is proportional to the junction area of the Schottky electrode, which is the junction area of the semiconductor rectifying device, whereby as a method to increase the cutoff frequency fc(=(2π×RsCj) −1) of the detecting device, decreasing the junction area of the semiconductor rectifying device may be considered.
For example, performing simple calculations of the Schottky barrier diode and cutoff frequency, if the junction area of the Schottky electrode is microfabricated to 1 μm2, then fc becomes approximately 300 GHz. If the junction area of the Schottky electrode is microfabricated to 0.1 μm2 which is one-tenth thereof (approximately 0.3 μm2 by when converted into terms of diameter), then fc becomes approximately 3 THz. Further, if the junction area of the Schottky electrode is microfabricated to 0.01 μm2 which is one-tenth thereof (approximately 0.1 μm2 when converted into terms of diameter), then fc can be estimated to be approximately 30 THz.
Japanese Patent Laid-Open No. 09-162424 discloses a detecting device that detects high frequency electromagnetic waves in this manner. According to Japanese Patent Laid-Open No. 09-162424, in detecting the high frequency electromagnetic waves, the junction area of a Schottky barrier diode which is a semiconductor rectifying device is microfabricated to 0.0007 μm2, and an electromagnetic wave of approximately 28 THz from a CO2 laser (wavelength 10.6 μm) is detected.
Thus, with a detecting device that detects electromagnetic waves using an antenna and semiconductor rectifying device as in the past, the junction area of the semiconductor rectifying device has been microfabricated in order to increase the cutoff frequency which is the frequency at the upper limit of the frequency band that can be detected. However, as the junction area of the semiconductor rectifying device decreases, the current flowing through the semiconductor rectifying device is limited, whereby the device resistance of the semiconductor rectifying device is increases. Particularly, in the case of a detecting device that detects electromagnetic waves of a 30 GHz to 30 THz frequency band, the device resistance results in at least several thousand Ω.